Recently, highly parallel processes have been developed for the analysis of biological substances such as, for example, proteins, peptides, nucleic acids (e.g., DNA, cDNA, etc.) and ribonucleic acids. Large numbers of different binding moieties can be immobilized on solid surfaces and interactions between such moieties and other compounds can be measured in a highly parallel fashion. While the size of the solid surfaces have been remarkably reduced over recent years and the density of immobilized species has also dramatically increased, typically such assays require a number of liquid handling steps that can be difficult to automate without liquid handling robots or similar apparatuses.
A number of microfluidic platforms have recently been developed to solve such problems in liquid handling, reduce reagent consumptions, and to increase the speed of such processes. Examples of such platforms are described in U.S. Pat. Nos. 5,856,174 and 5,922,591, which are hereby incorporated by reference in their entireties. Such devices were later shown to perform nucleic acid extraction, amplification and hybridization on HIV viral samples as described by Anderson et al., “Microfluidic Biochemical Analysis System,” Proceeding of the 1997 International Conference on Solid-State Sensors and Actuators, Tranducers '97, 1997, pp. 477–480, which is hereby incorporated by reference in its entirety. Through the use of pneumatically controlled valves, hydrophobic vents, and differential pressure sources, fluid reagents were manipulated in a miniature fluidic cartridge to perform nucleic acid analysis.
Another example of such a microfluidic platform is described in U.S. Pat. No. 6,063,589, which is hereby incorporated by reference in its entirety, where the use of centripetal force is used to pump liquid samples through a capillary network contained on a compact-disc liquid fluidic cartridge. Passive burst valves are used to control fluid motion according to the disc spin speed. Such a platform has been used to perform biological assays as described by Kellog et al, “Centrifugal Microfluidics: Applications,” Micro Total Analysis System 2000, Proceedings of the uTas 2000 Symposium, 2000, pp. 239–242, which is hereby incorporated by reference in it entirety. The further use of passive surfaces in such miniature and microfluidic devices has been described in U.S. Pat. No. 6,296,020, which is hereby incorporated by reference in its entirety, for the control of fluid in micro-scale devices.
An alternative to pressure driven liquid handling devices is through the use of electric fields to control liquid and molecule motion. Work in miniaturized fluid delivery and analysis has been done using these electro-kinetic methods for pumping reagents through a liquid medium and using electrophoretic methods for separating and performing specific assays in such systems. Devices using such methods have been described in U.S. Pat. Nos. 4,908,112, 5,858,804, 6,033,544, each of which is hereby incorporated by reference in its entirety.
Other miniaturized liquid handling devices have also been described using electrostatic valve arrays (U.S. Pat. No. 6,240,944, which is hereby incorporated by reference in its entirety), ferrofluid micropumps (U.S. Pat. No. 6,318,970, which is hereby incorporated by reference in its entirety), and a fluid flow regulator (U.S. Pat. No. 5,839,467, which is hereby incorporated by reference in its entirety).
While it is well understood that active, continuous mixing of chemical reactions greatly increases reaction rates due to the elimination of diffusion limiting conditions, most diagnostic products such as 96-well microwell plate kits and other automatic equipment still utilize static reactions. Typical attempts to increase reaction rates include increasing reaction temperatures, mechanical shaking, as well as ultrasonic agitation. As reaction volumes decrease in size it becomes more and more difficult to provide continuous mixing conditions. Alternatively, microfluidic devices can increase assay speeds by increasing surface to volume ratios. Static reactions on microfluidic devices, however, are still governed by diffusion limited reaction kinetics. Attempts have been made to improve reaction kinetics by continuously flowing reactants over active surfaces. See, for example, Cheek et al., 2001, “Chemiluminescence Detection for Hybridization Assays on the Flow-Thru Chip, a Three-Dimensional Micorchannel Biochip,” Analytical Chemistry 73, 5777–5783, which is hereby incorporated by reference in its entirety. This technique, however requires, large reactant volumes or extremely low flow rates. Back and forth motion has also been employed using a pressurized chamber to speed up reaction times. See, for example, Anderson et al., 2000, “A miniature integrated device for automated multistep genetic analysis,” Nucleic Acids Research 28, e60, which is hereby incorporated by reference in its entirety. The circulation method in a closed system has also been proposed for speeding up DNA hybridization reactions. See, for example, Chou et al., “Integrated Elastomer Fluidic Lab on a Chip—Surface Patterning and DNA diagnostics,” in Proceedings of the Solid State Actuator and Sensor Workshop, Hilton Head, S.C., 2000, which is hereby incorporated by reference in its entirety. While such a device is functional, it is somewhat unsatisfactory because it requires two pumps operating out of phase to enable circulation. The operation of two pumps operating out of phase adds expense to the chip.
The use of such miniaturized liquid handling devices has the potential to increase assay throughput, reduce reagent consumption, simplify diagnostic instrumentation, and reduce assay costs. Given the above background, what is needed in the art are improved closed system miniature fluid delivery and analysis cartridges.